Abortable mixed collections/Optional collections evacuate regions as time permits to better meet the pause time goal with evacuations. Another side-effect is to reduce garbage collections. The last time this has been done earnestly has been when the feature had been introduced.

Investigate on a few applications whether there is an impact and how large this is.

(Some) Interesting metrics are:
* how often is it used
* how well does this feature mark G1 meet pause time goals (from below and above)
* impact on total pause time

Candidates for this evaluation are BRT, extremem and specjbb2015 fixed-IR.

One option is to compare current implementation and setting the internal magic constant optional_prediction_fraction to 0, which will disable them.